Glucose facilitates cognition in a subset of Alzheimer's patients. Recent research indicates that a similar percentage of Alzheimer's patients have a deficit in mitochondrial DNA (mtDNA) which is responsible for the production of ATP. These findings suggest that the mtDNA deficit may differentiate between glucose responders and non- responders. The proposed experiment is a dose-response study of glucose facilitation of cognition in mtDNA normal and mtDNA deficient Alzheimer's patients using glucose clamping.